Lead frames are commonly used as a substrate for the packaging of integrated circuits. FIG. 1 illustrates a conventional lead frame 100 comprising a central die paddle 101 adapted for receiving an integrated circuit 110 and a plurality of leads 102 encircling the die paddle. The leads 102 which serve as electrical contacts are spaced away from the die paddle 101. In well known methods, an integrated circuit 110 is attached onto the die paddle 101 by dispensing a layer of epoxy glue 120 onto the die paddle 101 and attaching the lower surface of the integrated circuit to it. The epoxy glue is then cured to hold the integrated circuit securely in place. Following this, wire bonds are formed to electrically connect the electrical contacts located on the upper surface of the integrated circuit (not shown) with respective leads 102 of the lead frame. The integrated circuit 110, die paddle 101 and wire bonds are subsequently encapsulated in an electrically insulating resin and the leads 102 cut leaving portions of the leads extending out of the resin body so that they may be connected to further circuitry.
Unfortunately, the above described conventional lead frame design 100 and packaging method deployed suffers from a number of problems. First of all, the dispensing of epoxy glue and placement of the integrated circuit 110 has to be carefully controlled in order to avoid problems such as excessive glue bleed, glue void and die tilt. For example, if the amount of epoxy glue dispensed is too great, the epoxy glue may leak from beneath the integrated circuit 110 and cover some of the electrical contacts of the integrated circuit or inner ends of the leads 102 where the connecting wires are bonded. In this case, it may be impossible to form reliable wire bonds between the electrical contacts of the integrated circuit and the leads of the lead frame. In addition to this, the epoxy glue cure process also introduces additional problems such as out-gassing of parts used in the glue cure process, glue cure oven contamination and the need to control complex glue curing profiles. Aside from the above packaging problems, there are also concerns from the reliability point of view as the conventional integrated circuit packages formed are found to be susceptible to delamination effects during subsequent use. This is because delamination between the resin body and die paddle are often observed after the package has been subjected to accelerated reliability testing such as temperature cycling and pressure cooker test. The glue region 120a in particular is especially prone to delamination.
As a result of these problems associated with the conventional lead frame design and packaging methods, the packaging yield and reliability of the resulting integrated circuit packages formed are severely compromised. It is an object of the invention to provide a lead frame design and packaging method which alleviates these problems and/or provides the general public with a useful choice.